Geochemistry of stream sediments as a tool for assessing contamination by Arsenic, Chromium and other toxic elements: East Attica region, Greece

Geochemistry of surface hyporheic stream sediments, multivariate statistics and GIS database proved successful tools for assessing toxic element contamination in East Attica region. The objectives of this study were to assess the degree of contamination and to describe the surface hyporheic stream sediment geochemical variations in relation to geology, lithology and anthropogenic activities of East Attica region. The type of methodology used in this study consists of chemical analysis, pH evaluation, mineralogical analysis, cumulative probability plots, factor analysis, GIS database and comparison of the stream sediment contents with standards and levels recorded in the literature. The results of the study about stream sediments of East Attica region are presented. Cumulative probability plots in combination with spatial representation provided a clearer answer to the East Attica threshold question. The threshold values of East Attica streams are: As 20 mg kg, Cd 0.3 mg kg, Co 13 mg kg, Cr 225 mg kg, Cu 17 mg kg, Mn 400 mg kg, Ni 120 mg kg, Pb 40 mg kg, Sb 0.8 mg kg and Zn 70 mg kg. Relationships between various elements have been identified from factor analysis and reflect genetic associations. Factor analysis of the stream sediment data establishes eigenvalues that account for 85.8 % of the total variance and separates elements into three factors: Factor 1, an association of As, Ba, Cd, Fe, Cu, Fe, K, Mn Pb, Sb and Zn; Factor 2, an association of Co, Cr, Cu, Fe, Mg and Ni; and Factor 3, an association of Al, As, Ba, Co, Cu, Fe, K, Mn and Sb. A GIS elaboration showed the spatial relationship between high positive factor scores and presence of ore deposits and anthropogenic contamination. The sulphide and manganese-iron mineralization, small bodies of metabasic rocks and ophiolite fragments within Neogene-Quaternary deposits are the main components of toxic elements in East Attica surface hyporheic stream sediments. The composition of stream sediment is modified by contribution of various anthropogenic sources. There is both natural and anthropogenic input of As in East Attica streams, while there is a natural contamination of surface hyporheic stream sediments of East Attica region where natural elevated Cr and Ni surface hyporheic stream sediments contents exceed the Soil Guideline Values established by the Environment Agency.